1. Technical Field
This invention relates to people moving devices in general, and more particularly to people moving devices which employ a step chain.
2. Background Art
Escalators are a known method for conveying people from a first elevation to a second elevation. Typically, an escalator includes a frame, a drive, a step chain and a pair of balustrade assemblies. The frame comprises a truss section on both the left and right hand sides of the frame. By convention, the side of the escalator on the left of a person facing the escalator at the lower elevation is called the left hand side of the escalator, and the side to the person's right is called the right hand side. Each truss section has two end sections parallel to one another, connected by an inclined midsection. The end sections form landings at the two elevations connected by the midsection, one on each end. Matching pairs of roller tracks are attached on the inside of each truss section, i.e. the side of the truss section facing the other truss section.
The escalator drive is attached to the frame in the upper landing, between the trusses. The drive typically drives a step chain sprocket assembly consisting of a pair of step chain sprockets, a pair of handrail sprockets, and an axle extending from one side of the frame to the other. The two step chain sprockets power a step chain formed in a loop running from the first elevation to the second elevation.
The step chain consists of a pair of chain strands, having a plurality of rollers, and a plurality of connecting axles for connecting the two chain strands. Each strand is formed from a plurality of chain links. Each link has a pair of side plates, an axle, and a roller. The axle is received in the center of the roller. A side plate of the link and a side plate of the next link in line, are attached to the axle on both sides of the roller, thereby holding the roller and axle together. This link arrangement is repeated as many times as is necessary to arrive at the length strand, and therefore the length chain, desired.
Every "n.sup.th " link in the strand is connected to the aligned strand on the other side of the frame. Connecting the axles together ties the two independent strands into a single step chain. One strand of the step chain rides a roller track on the right side of the frame and the other strand rides the matching roller track on the left hand side of the frame. Each pair of connected rollers provides the support for one tread plate.
The rollers may be connected in a number of different ways. First, it is known in the art for the aligned rollers to share a common axle. The common axle extends through the two aligned links, acting as a single axle for the aligned rollers. Another method incorporates strands having aligned stub axles which extend out a specific distance toward the other strand. In a first embodiment, a tread plate receives each stub axle in a bore on that side of the tread plate, thereby connecting the aligned stub axles. In a second embodiment, a connecting axle independent of the tread plate receives the aligned stub axles. The stub axles are press fit into bores on the ends of the connecting axle and the tread plate is attached to the connecting axle. In a third embodiment, the tread plates are directly attached to the stub axles. A connecting axle, independent of the tread plate, receives the aligned stub axles on the inside of the tread plate. Holes are drilled in the connecting axle and the stub axles to receive pins. The pins fix the connecting axles to the stub axles.
All of these methods of connecting the aligned rollers have distinct disadvantages, however. First, step chains having a common axle between aligned rollers have a fixed width and therefore cannot be readily interchanged between different width escalators. Moreover, if a common axle becomes damaged, both strands must be disassembled to repair the chain.
Second, using stub axles connected by tread plates alone creates an undesirable loading on the roller bearing. The yoke of the tread plate attaches to the unsupported stub axle outside of the centerline of the roller bearing thereby creating a cantilever type arrangement. As a result, the roller bearing experiences not only a load, but a moment as well. The combination of load and moment create an undesirable stress on the roller bearings which negatively effects the B.sup.10 life of the bearings. Increased maintenance frequency on an escalator seriously diminishes the desirability and quality reputation of the escalator.
In the case of the press fit connecting axle, the disadvantage lies in the difficulty of assembling and disassembling the step chain in the factory and especially in the field. To get the proper press fit, the connecting axle and the stub axles must either be forced together or the connecting axles must be heated and sweated onto the stub axles. Either way, the process is time consuming and difficult to disassemble in the field.
Finally, attaching the tread plate to the stub axles and pinning the connecting axle to the stub axle is also disadvantageous. Pinning the connecting axle necessitates holes being drilled either at assembly or during the manufacturing of the separate pieces. In the former case, drilling every connecting axle at assembly is a labor intensive and time consuming function. In the latter case, alignment of the bores must be precise or an interference will occur. The potential for undesirable error, either way, is present during the assembly process.